Strange video levels when scaling

[Qframe]

Hi there,

Has anyone experienced strange sub 0% video level 'noise' I suppose you could call it, in video that has been scaled?

For example while working in a SD timeline, if you import a HD clip and scale it using Scale in the motion tap,  the Lumetri scopes show that the waveform gets pulled apart and some of the 'black' elements are dragged down below 0%, some as low as -20%. The application of a the Video Limiter has no effect in correcting the levels.  While dragging the time bar the levels move back up then re-appear when stopped.  I thought it might just be a monitoring issue but if the timeline is exported the level issue remains in the exported clip (import back in to test). Obviously you need to have 'Clamp Signal' unchecked on the scopes to see it.

Even when down-converting on export (Media Encoder) the levels are messed up.  Basically if video is been resized the levels are effected.

Hopefully the following images will demonstrate the problem. The first image shows an 'unscaled' clip.  The waveform is normal (blacks a little low for broadcast). The second image shoes the same video frame scaled down to an arbitrary size of 90%.  You can now see that the levels are extending down and some movement in the rests of the image wave form.  Third image is a CU of the waveform.

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Hopefully someone can shed some light on this problem. Up until now we were using Premiere for broadcast work but this issue creates 'illegal' video levels for broadcast. We have used DiVinci Resolve to re-correct the levels but it is putting another conversion in workflow. We have other editing software on the machine that don't suffer from this problem.

Currently we are using an iMac with High Sierra OS and the latest Prem Pro version.  The same problem occurs on our brand new Macbook Pro with latest software so it seems that it's a Premiere problem.

[chrisw44157881]

8 bit can't go lower than 0. it might be remapping a bug and the scopes may be wrong. what do the scopes say in resolve?

would this work?

premiere pro cc 2015.2 broadcast safe preset - Creative COW

[Qframe]

Thanks,

I'm not an expert on Resolve but I think it corrects the levels. I don't know how to make it show below 0.  When I export out of Resolve and import back to Prem the 'noise' is gone and all of the levels are correct again.

A Broadcast content provider had a look at one of my files and they are seeing the same below 0 signal. They will not approve it for broadcast.

Now sure how to proceed here, it looks as though Premiere won't work for us in for broadcast material.

[francis-crossman · Accepted solution]

This is a known issue that we are working on.  The workaround, for now, is to nest your sequence and apply the video limiter on the nested sequence. Also, in Media Encoder you can apply the video limiter from the "Effects" tab.  Both methods will clip the undershoots and produce broadcast legal video without affecting the image.

[Qframe]

Thanks for letting us know that it's not our systems. We look forward to the problem being remedied in the next update.

[gw009]

this work around does not work when exporting to mpeg2.

as you can see - the mpeg2 still has the black level problem even with workaround suggested applied.

any other suggestions? and any idea when this bug will be rectified.

[gw009]

"This is a known issue that we are working on.", well it still is an issue with the new version of prem 13. any chance adobe could actually fix this problem?  this is a pain for broadcast professional using prem.